On Monday June 24 at 14:00 we have the pleasure to welcome Jacob Torrejon from SPEC, CEA Saclay, France. He will give us a seminar at CEA/IRIG, Bat 1005, room 445 entitled :
Chiral magnetism controlled by spin-orbit torques and spin-torque nano-oscillators: From magnetic memories to neuromorphic computing
Electrical manipulation of the magnetization (uniform or magnetic textures) by spin- polarized current is essential for developing advanced storage class memory devices . In ultrathin magnetic heterostructures with large spin-orbit coupling and broken inversion symmetry (ultrathin magnetic layer attached to heavy metal underlayer), new mechanisms has emerged based on spin-orbit coupling phenomena which exhibits much higher efficiency than conventional spin transfer torque mechanism in magnetic tunnel junction . Key to the power efficient magnetization control is the large spin-orbit coupling of the heterostructure. First, the spin Hall effect (SHE) induced by the heavy metal layer which generates large spin current exerting a torque on the adjacent magnetic layer . And second, the Dzyaloshinskii- Moriya interaction (DMI) which promotes Neel walls with fixed chirality and allows very efficient and fast domain wall motion . In the first part of my seminar, I will describe in detail the two spin-orbit coupling mechanisms, SHE and DMI, discussing several experimental techniques used for the quantitative estimation of both phenomena . Although magnetic memories are the most straightforward application of spin transfer and spin-orbit torques, magnetic tunnel junction can operate as tuneable non-linear nano- oscillators under different bias conditions (current and magnetic field). These devices called spin torque nano-oscillators have been proposed as new RF sources  and very recently for neuromorphic computing  inspired in the complex non-linear dynamical behaviour displayed in our brain . Indeed these observations have inspired a whole class of models based on non-linear oscillators networks able to perform cognitive tasks . However this type of computing requires a huge number of oscillators for achieving excellent performance and nanoscale oscillators with low noise are necessary for easy integration in a microchip. Spin torque nano-oscillators are very promising building block for neuromorphic computing because their well-controlled magnetization dynamics leading to high signal to noise ratios, their exceptional ability to interact, non-linear tunability by spin torques, fast time response (ns range), long lifetime and lower power consumption . In the second part of my seminar, I will show how to leverage the non-linear dynamics of spin-torque nano-oscillators for neuromorphic computing, and present our first experimental achievements of speech recognition task  and temporal pattern recognition with delayed feedback memory . Finally, I will give the main ingredients towards massively parallel architectures.
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